User's Manual

PMAC User Manual
18 Getting Started with PMAC
Type J<CR> and the motor should stop. If it takes a while to stop, either slow down the move next time or
increase I130 to reduce the error. J-<CR> should cause the motor to turn in the negative direction, and
J<CR> should stop it again. J=<CR> should cause the motor to jog to the last pre-jog position and stop
there automatically.
Optimizing Jog Performance
If your jog speed seems slower than desired, one or more of PMAC automatic safety limit parameters may
have been used, particularly if there is a fine-resolution system. The first of these is I119, which is the
maximum permitted motor jog acceleration, expressed in counts/msec
2
. The default value is quite low for
most systems. Increase it several orders of magnitude for now to get it out of the way.
Velocity Feedforward Gain
When jogging at constant speed, monitor following error and increase velocity feedforward gain (I132) to
minimize the following error. If there is a current-loop amplifier, set I132 equal to I131 or just slightly
greater.
Integral Gain
To eliminate steady-state error, bring in some integral gain. Set I133 to 10,000. This should provide weak
integral action, but enough to eliminate steady-state error over a few seconds. Now try increasing I133
some more to get quicker action. It should be safe to raise it in increments of 10,000 to get the performance
needed (quick restoration of commanded position without introducing oscillation). If there is oscillation,
reduce the integral gain until the oscillation is eliminated.
If there is no effect from adding integral gain, check the integration limit parameter I163. If this is low
(100,000 or less), it will limit what integral gain can do. If this is the problem, set this parameter to its
default value by typing I163=*<CR>.
Power-Up Mode
For future power-up/reset cycles, set I180 so power up is done in the mode wanted. If I180 is zero, Motor
#1 will power up "killed" (0V output, AENA signal false). It will not attempt to control until a servo
command is given (usually J, A, or <CTRL-A) for a non-PMAC-commutated motor, or a $ command for a
PMAC-commutated motor. This I-variable must be stored in non-volatile memory (with the SAVE
command) to be effective at the next power-up/reset cycle.
Homing Search Move
To do a homing search move, first check the position-capture I-variables (I902 and I903 in the example).
Make sure they are set up to capture the position where the home position should be. With a bare motor,
only use the third channel of the encoder. Set I902 to 1 to force a capture on the rising edge of the third
channel.
Next, set the homing speed with I123 (in units of counts/millisecond). Changing the sign of I123 changes
the direction of the homing move. Homing accel/decel is controlled by I120 and I121 (which also affect
jog moves). Now command a homing move with the HM command, and the motor will move as specified
until the proper signal edges is found, then decelerate to a stop and come back to the position of the trigger,
plus or minus an offset amount determined by I126.